1. Field of the Invention
The present invention relates to screens for windows, doors and the like, and in particular, to a screen retention assembly for securing a screen to a frame or surround. The invention presented is primarily intended for security screens that deter human intruders and provide impact protection from flying debris. However, the system may also be used for security screens that prevent the intrusion of insects and small animals into a building.
2. Background of the Invention
Doors or windows incorporating a semi-transparent screen or mesh provide the advantages of visibility, ventilation, and also the ability to prevent the passage of insects or small animals through the aperture covered by the screen. Screens are typically made from a flexible wire mesh although other flexible or semi-rigid perforate sheet materials may be used.
Common prior art screen systems attach the mesh directly to the perimeter of the window or door opening with simple fasteners such as screws, rivets or glue. While such systems are functional, they lack a means of applying tension to the screen upon installation. A tensioned screen is important because ordinary use of a door or window often causes repeated impact loads to the screen, for example pushing the door open by pushing or kicking the screen. Thus, the semi-rigid material of the screen often appears floppy after a short period of ordinary use.
The strength and appearance of a screen attached using simple fasteners is also overly dependent on the skill of the fabricator. For example, if the screen is cut slightly too small, the screen will be weakened and subject to pulling out of the frame because the fasteners will be too close to the edge of the mesh. If glue is used, it will not sufficiently cover enough surface area of the mesh to create a strong bond. On the other hand, if the screen is cut slightly to large, then the mesh will be unavoidably floppy because the use of simple fasteners provide no means for tensioning the mesh.
To overcome many of the weaknesses of directly fastening a screen to the perimeter of a window or door opening, more modern systems that frame the openings with extruded metal, typically aluminum, channel sections have been developed, wherein the edges of the screen are secured within the channel walls. A wide variety of means for securing screens within the channel walls have been developed. Prior art systems range from simple friction fits between the screens and the channels to complex turnbuckle like fasteners mounted in the channels which grip and tension the screen.
Screen retention systems that feature channel section frames about the perimeter of door or window opening have effectively overcome many of the drawbacks of systems that attached the screen directly to the door or window frame. Aesthetic appearance has been improved due to the lack of visible fasteners. Function has also been improved because some of the prior channel section screen retention systems have some ability to tension the screen.
Prior an channel-based screen retention systems do suffer from certain drawbacks however. In particular, prior art systems typically use flat or screen edges which allow for only a very limited amount of screen tensioning and offer only modest resistance to screen impact loading. When screen tensioning provisions are specifically provided, they nevertheless often have a very limited adjustment range. In addition, many prior art screen retention systems allow the metal of the screen, typically iron or steel, to contact the wall of the, typically aluminum, channel. This contact of dissimilar metals allows for galvanic corrosion at the interface between the screen and the channel. Power coated stainless steel is the preferred material for security screens. Common insect screens are typically made using vinyl coated fiber glass, aluminum mesh, galvanized steel, bronze, stainless steel, or vinyl coated polyester.
What is needed in the art is an improved channel-based screen retention system that provides a more secure attachment of the screen within the channel to provide increased resistance to screen impact loading. Also desirable is a broader range of screen of tensioning adjustment and for a design that electrically isolates the screen from the walls of the channel, when the channel and screen are both made from metallic materials as is commonly the case.